First-principles prediction of carbon monoxide nanotube bundles in low pressure phase

Abstract

The crystal structure of carbon monoxide has been studied for more than half a century. The internal structures of low-pressure carbon monoxide crystals have been investigated by means of infrared analysis and Raman analysis, and the internal structure of carbon monoxide has also been studied through computational analysis. Previous studies showed that carbon monoxide can produce different phase transitions at different pressures, and thus forming new polymers with new physical properties such as electrical, optical and mechanical properties. In this paper, from first-principles calculations, we propose six nanotube structures made of carbon monoxide, named Tube-3–Tube-8. The nanotubes are packed into the nanotube bundles, and carbon monoxide nanotube bundle structures that are similar to carbon nanotube bundles are constructed by first-principles calculation. We study the structural, energy and electronic properties of the nanotubes and nanotube bundles. In order to evaluate the relative stability of the predicted nanotubes, we calculate the cohesive energy and phonon spectrum, and we also carry out the molecular dynamics analysis. The results show that there are three nanotubes (Tube-4–Tube-6) that are relatively stable, of which Tube-5 nanotube is the most stable phase. We attribute the stability of Tube-5 to sp³-hybridized C atoms being nearest to the hybridized atoms of diamond. Then we investigate nanotube bundles from the three stable nanotubes, and accordingly name them Bundles-4–Bundles-6. We calculate the enthalpy function under pressure and compare it with the enthalpy function of several known carbon monoxide molecular crystal and chain crystal, which are the most stable structures according to the current studies. More pleasingly, we find that these nanotube bundles are more stable than these carbon monoxide molecular crystal and chain crystal at low pressure. In addition, by calculating the energy bands of Tube-4–Tube-6, we can deduce that these nanotube bundles (Bundles-4– Bundles-6) are all wide band gap semiconductors, which are entirely different from molecular and chain crystals that are metals. We expect that the discovery of nanotube bundle structures will increase the diversity of carbon monoxide crystal under low pressure, and provide a new understanding of exploring the internal structure of carbon monoxide crystal.